well i think in general the horizontal fist requires you to turn you r hand from the on guard position, creating torque and bunching up the skin , and the verticle fist is exceptional for hooks, becaust all 4 knucks can land on the chin.

Firstly you cannot chain punch with horizontal fists. And if someone can land 3-4 solid punches a second with a vertical fist then I would say tha vertical is the way to go. However the horizontal may be more powerfull due to the twisting torque (a theory which has not been proven to me and to which i remain dubious), and i like using a horizontal for hitting to the ribs, you get a more wide area of rib and you can push it up with your knuckles, which is a killer!

It varies with the technique. If I'm using a boxing hook, of course my fist will be vertical, because that is the technique. But something like a karate punch from the horse stance, something I don't practice, would include a horizontal fist. Wing Chun's chain punching techniques using vertical fists are very effective, as well as the "Boxing Blast", comparable to the straight blast, but with modifications.

It all relates very scientifically, The Tao Of Jeet Kune Do is a great book to read defining scientific approaches and influences in the martial arts.

If I may Chime in I believe that the verticle fist may be faster and of better uses closer but the horozital fist can be delivered with more power from regular punching range, I use the veritcle fist if I need to strike at quarter distance range, the palm up strike if closer, and the horozital fist if to go over or around and in between the chin and trecha (really I use a fore knuckle/leapord paw strike for that).

Some people believe that the horozital fist is more prone to having the elbow snapped/slapped during the strike, because the elbow turns over to the side. Goju practitioners teach to retract/bend the elbow after fully extending the punch because of this counter against the elbow.

I find the sensation different both. With the vertical fist I find the impact to be blunt and more of a thudding force, very deep and dull. With the horizontal fist I find the impact very sharp, cracking and cutting sensation.

A friend of mine and former Kempo instructor was also a very experienced Wing Chun practitioner. He described the difference between the two styles of punching as the wing chun being like a machine gun and the karate being like a rifle. Both different in their approach, but equally deadly.

dependin on the situation...vertical fist is used more for speed and the true power comes from the speed that comes from your vertical punch. horiziontal fist is basically for power attacks.

i say...in a real situation of combat, vertical fists would be the best. i say this is becuz of speed, combat is all about speed. On the other hand, if your opponent leaves open gaps and is slow, go for horizontal fists, it puts more impact into it, but the attack would not be as rapid as consecutive vertical fist attacks. Therefore, my point being, vertical go for speed, horizontal go for power.